Abstract

Detailed 2D measurements of long-wavelength density fluctuations in the pedestal region with beam emission spectroscopy during the period between edge localized modes(ELMs) indicate two distinct bands of fluctuations propagating in opposite poloidal directions in the plasma frame: one lower frequency band (50–150 kHz) advects in the ion-diamagnetic drift direction (ion mode) and a higher frequency band (200–400 kHz) advects in the electron diamagnetic drift direction (electron mode). The ion mode amplitude is modulated with the ELM cycle: it increases rapidly after an ELM and then saturates, similar to the evolution of the pedestal electron pressure and density gradients. The electron mode, in contrast, has no significant time evolution between ELMs. The decorrelation time of the ion mode is <5 [], the radial correlation length is of order 10 and has poloidal wave-number , and the mode advects at near the ion diamagnetic velocity in the plasma frame. These spatiotemporal dynamics are qualitatively similar to features predicted for kinetic ballooning modes.

Received 15 December 2010Accepted 13 April 2011Published online 26 May 2011

Acknowledgments:

This work was supported by the U.S. Department of Energy under DE-FG02-89ER53296, DE-FG02-08ER54999, DE-FC02-04ER54698, and DE-FG02-95ER54309. The authors appreciate the support of the DIII-D team and valuable discussions with Professor J. D. Callen.